It has been reported that high-intensity discharge (HID) lamps, such as high-pressure, mercury-vapor lamps, can constitute a safety hazard to people in close proximity to the lamps if the protective outer envelope is broken permitting short wavelength ultraviolet radiations to escape.
A number of lamps containing safety devices for preventing people from being exposed to short wavelength ultraviolet radiations have been developed. One such lamp is disclosed in U.S. Pat. No. 4,013,920 dated Mar. 22, 1977, issued to John Petro. This lamp utilizes a resilient safety switch positioned proximate the inner surface of the dome portion of the protective outer envelope in contact with an extremity of a resilient leaf-spring support portion of the arc tube frame to maintain the switch in a closed position. When the envelope is shattered the normally closed switch will open to break the electrical path to the arc tube, thereby rendering the lamp inoperative.
U.S. Pat. No. 4,013,919 dated Mar. 22, 1977 issued to Corbley discloses a fuse heater and shunting thermal switch connected in series with the arc tube and located within the outer envelope. If the outer envelope is broken, air cools the switch so that it opens. Current flow through the heater raises the temperature and causes it to oxidize, thereby opening the circuit and disabling the lamp.
Russian Pat. No. 1,322,142/24-7 published Apr. 2, 1970 by Sulatskov et al. discloses a high-pressure discharge lamp incorporating a cerium-containing link which oxidizes when exposed to air and breaks to open the arc tube energizing circuit, thereby preventing the emission of UV radiation upon the breakage of the outer envelope.